System and method for calibration of a wireless network

ABSTRACT

In one embodiment, the present invention is a method and system for calibrating a wireless network including a Mobile Switching Center (MSC), and a Position Determination Device (PDD). The wireless network is capable of determining the position of a handset. The method includes receiving a trigger from the MSC; sending a position request message to the PDD in response to the received trigger; receiving a position request response message from the PDD; continuously sending subsequent position request messages to the PDD in response to the same received trigger, until a termination command is received; terminating the sending subsequent position request messages, when the termination command is received; and generating output data including network calibration parameters.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.10/634,407, filed Aug. 5, 2003, which claims the priority of U.S.Provisional Patent Application No. 60/401,164, filed Aug. 5, 2002. Thecomplete disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a wireless communication network. Morespecifically, the present invention relates to a method and apparatusfor generating calibration data for positioning determination systems inwireless networks.

BACKGROUND OF THE INVENTION

Wireless networks can determine the position of a mobile device based ontrilateration using, for example, time difference measurements taken bythe wireless handset, or by components installed in the wireless networkor adjunct to it.

The challenge of trilateration on wireless signals, e.g., in PCS andcellular networks, is that those networks have transmitters and/orreceivers that are either unsynchronized or loosely synchronized to atiming reference that is of insufficient accuracy to support locationvia trilateration. This problem can be corrected by calibrating thewireless network and/or Position Determination Device to determine thesecalibration values and in turn subtract their effects from subsequentposition calculations.

Calibrating a network can be an expensive and time-consuming process. Inorder to achieve statistical significance, many calibration data samplesare required. Traditional methods utilize a substantial amount of testequipment to obtain the necessary calibration data. A typical methodrequires the tester to generate a significant number of calls from awireless handset. Each call is received by the Mobile Switching Center,which forwards the call to another device that accepts the call andissues one Position Request message per call, generating a singlePosition Response Only one calibration sample is generated per PositionResponse, therefore many calls are required to generate a sufficientnumber of samples. To generate the number of Position Requests requiredfor statistical significance, the tester must make an equal number ofcalls, which is generally time consuming because the tester has noknowledge of when the Position Response was received by the device thatissued the Position Request. The limiting factor is that thistraditional method generates only one calibration sample per invocationof the Position Determination process when used for calibrationpurposes.

A calibration sample is defined herein as a measurement of thedifference between an absolute time reference, and the actual timereference being used by the components in the wireless network. Eachreference point in a wireless network can be associated with an observedtime, and the calibration value associated with that reference point issubtracted from the observed time reference to achieve a referencecloser to absolute time. The calibration value is comprised of manycalibration samples via averaging or other statistical methods.

SUMMARY OF THE INVENTION

The present invention is a method and system for network assistedcalibration (NAC) in a wireless network. The NAC method and system causea Position Determination Device to rapidly generate wireless networkcalibration data. This calibration data is generally used to improve thelocation accuracy of position determination systems that rely ontrilateration within cellular networks. When integrated with a wirelessintelligent network, the system of the present invention assumes therole of a messaging system and wireless call-taking device (landlinevoice or data network) during calibration calls that autonomously causesthe rapid and efficient generation of calibration data.

In one embodiment, the present invention is a method and system forcalibrating a wireless network including a Mobile Switching Center(MSC), and a Position Determination Device (PDD). The PDD within thewireless network is capable of determining the position of a handset.The method includes receiving a phone call from the MSC; sending a firstposition request message to the PDD responsive to the received phonecall; receiving a position request response message from the PDD;continuously sending subsequent position request messages to the PDDcorresponding to the same received phone call; terminating the sendingof subsequent position request messages, when a termination trigger isreceived from the MSC; and sending a call termination message to the MSCin response to the received termination trigger.

In another embodiment, the present invention is a method and system forcausing generation of calibration data in a wireless network including aMobile Switching Center (MSC), and a Position Determination Device (PDD)to determine position of a handset. The method includes receiving atrigger from the MSC; sending a position request message to the PDD inresponse to the received trigger; receiving a position request responsemessage from the PDD; continuously sending subsequent position requestmessages to the PDD in response to the same received trigger, until atermination command is received; terminating the sending subsequentposition request messages, when the termination command is received; andcausing the generation of output data for use in network calibration.The trigger may be generated by a call origination message from the MSCor by a received call from the handset. Moreover, the terminationcommand may be a call termination message from the MSC, or thetermination may occur when the call origination message from the MSC isreleased.

Still other embodiments of the present invention will become readilyapparent to those skilled in the art from the following detaileddescription, wherein is shown and described only embodiments of theinvention by way of illustration of the best modes contemplated forcarrying out the invention. As will be realized, the invention iscapable of other and different embodiments and its several details arecapable of modification in various obvious respects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary illustration of position determination in awireless network;

FIG. 2 is an exemplary architecture used to enable location services ina wireless network;

FIG. 3 is a network reference model for a wireless Phase 2 911;

FIG. 4 is an exemplary block diagram of a system for network assistedcalibration, according to one embodiment of the present invention;

FIG. 5 is an exemplary block diagram of a system, according to MessagingOnly embodiment;

FIG. 6 is an exemplary process flow diagram, according to Messaging Onlyembodiment;

FIG. 7 is an exemplary state diagram, according to Messaging Onlyembodiment;

FIG. 8 is an exemplary block diagram of a system, according to Call Pathembodiment;

FIG. 9 is an exemplary process flow diagram, according to Call Pathembodiment;

FIG. 10 is an exemplary state diagram, according to Call Pathembodiment;

FIG. 11 is an exemplary block diagram of a system, according to Hybridembodiment;

FIG. 12 is an exemplary process flow diagram, according to Hybridembodiment;

FIG. 13 is an exemplary state diagram, according to Hybrid embodiment;and

FIG. 14 is an exemplary log file, according to one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an exemplary position determination configuration 100in a wireless network. The configuration 100 includes wireless sites (orbase stations) 102, 104, 106 with known positions and a wireless handset114 with an unknown position. Once the time difference measurements 108,110 and 112 between the wireless sites 102, 104, 106 and the wirelesshandset 114 are performed, the handset position can be determined bytrilateration from known positions of the wireless sites 102, 104, 106.In practice, wireless sites within a location determination systemoperate according to local timing references. These timing referencesmay not be exactly the same for each wireless site, and the resultingoffsets cause some amount of error in the location computation.

Calibration is a process that reduces this position error by comparingthe time reference of each wireless site to a common reference toaccount for the timing differences. The calibration process may utilizethe actual measurements used for trilateration and positioning when thelocation of the wireless handset is already known, because thepropagation delay between each wireless site and the handset can becomputed based on the respective location of each. By using thesemeasurements to calibrate the location determination system, locationaccuracy can be significantly improved.

For example, in realization of Phase-2 911 and other location basedservices, the network elements typically involve one or more of thefollowing generic devices: Mobile Switching Center, Mobile PositionGateway and Position Determination Device. The Mobile Switching Centeris responsible for call routing and managing the setup and teardown ofvoice circuits. The Mobile Position Gateway assists the Mobile SwitchingCenter in determining how to route the call. The Position DeterminationDevice is responsible for calculating the position of the mobilehandset.

The basic architecture for a wireless network enabled with locationcapabilities is illustrated in FIG. 2. In this representation, theMobile Switching Center 202 includes the wireless sites (base stations)connected to it directly or through a base station controller. Theprimary responsibility of the Mobile Switching Center 202 is routingtelephone calls to and from the wireline voice or data network 204. TheMobile Position Gateway 206 manages location information for wirelesshandsets, and provides an interface for external devices including thewireline network 204 to request position information. The PositionDetermination Device 208 is responsible for calculating the location ofa wireless handset, and communicating the position information to theMobile Positioning Gateway 206 for management and distribution of thelocation information. These elements are part of the wirelessintelligent network that enables operation of radio and locationservices, such as, those utilized in cellular telecommunications.

One embodiment of such a wireless network is realized in WirelessPhase-2 911 services, in which emergency callers are located for theentity that receives the emergency call. This architecture isillustrated in FIG. 3. As shown, the Mobile Positioning Center (MPC)306, and Position Determination Entity (PDE) 308 are respectiveembodiments of Mobile Positioning Gateway 206, and PositionDetermination Device 208 of FIG. 2. The Emergency Services Network 304is one embodiment of the wireline voice and data network 204 (of FIG.2). In FIG. 3 the AiDi interface is used to carry voice conversationsover a “call path” between the MSC and the Emergency Services Network.The E3 interface is used by the MSC to request call path utilizationinstructions from the MPC using “messaging”. The E5 interface is used bythe MPC to request position from the PDE, also using messaging. The E12is a third messaging interface used for communication between the PDEand a handset, which is carried through the MSC. The Emergency ServicesNetwork corresponds to a specific application, namely Phase 2 911services that utilize location to assist emergency callers. When itreceives an emergency call on the AiDi interface, it uses messaging onthe E2 interface to request position from the MPC. For PSC 1900 or GSMand UMTS networks, the Gateway Mobile Positioning Center and ServingMobile Location Center act as the Mobile Positioning Gateway 206 andPosition Determination Device 208, respectively.

When a call that requires location identification is initiated on awireless network, such as for Phase-2 911 services, intelligent networkmessages are exchanged between network devices over signaling interfacesto instantiate call setup procedures. When a call is placed to afacility that requires location capabilities, certain embodiments ofthese messages are exchanged to request and respond with the calculatedlocation of the wireless handset. The messages of interest in this caseare termed generically: Call Origination messages, Call Terminationmessages, and Position messages. These messages can be of either aRequest or Response variety.

Call Origination Request messages are typically exchanged between theMobile Switching Center 202 and other network devices. They are used tonotify other network elements that a call is being setup and to requestservices to assist in this task. Call Termination messages are exchangedbetween the Mobile Switching Center 202 and other network devices. Theyare used to notify other network elements that a call has terminated andresources associated with this call can be released.

Position messages are exchanged between the Mobile Position Gateway 202and the Position Determination Device 208. They are used to request andrespond with the calculated position of a handset. Position messages arealso exchanged between the Mobile Position Gateway 206 and the wirelinevoice and data networks 204 (e.g. an Emergency Services Network 304 inFIG. 3) tasked with retrieving caller location. These messages are alsoused to request updates of a handset's position.

When the Position Determination Device has been implemented within awireless network, the wireless network infrastructure and handsetssupport some form of trilateration, wherein the position of the handsetis also determined through another independent process, for example,Global Positioning System (GPS). In one embodiment, in order to triggerthe NAC process, a calibration call is placed from a wireless handset toa standard telephone or to the NAC system. The NAC system describedherein assumes the responsibility of the Mobile Position Gateway and incertain embodiments the wireline voice or data network for calibrationcalls. More importantly, the system enables the rapid generation ofcalibration data as described in the paragraphs that follow.

One of the differences between the present invention and the MobilePosition Gateway is that the present invention enters a “loop” processwhereby it autonomously generates multiple position request messages tothe Position Determination Device per calibration call. However, fornormal calls, the Mobile Position Gateway is only permitted to generatea single position request message per call and does not have any callinterface. Another difference between the present invention and theMobile Position Gateway is that the present invention also acts as acall-taking device. The processes of this call-taking device (asexplained later) closely coupled with the NAC's messaging engine effectthe rapid generation of data required for calibration.

FIG. 4 is an exemplary block diagram of a NAC system, according to oneembodiment of the present invention. As shown, there are two interfaces:the Call Interface 402 used for handling voice or data calls forwardedfrom the handset 114 through the Mobile Switching Center 202, and theMessage Interface 404 used for handling messages to and from the MobileSwitching Center 202 and the Position Determination Device 208. Theinterface between the Mobile Switching Center 202 or the PositionDetermination Device 208 and the handset 114 are outside the scope ofthis embodiment of the NAC system. The NAC system 400 also includes twocore elements, the Call Processing engine 406 and the Message Processingengine 408. The Call Processing engine 406 accepts voice or data callsand provides voice or data status information to the handset over thecorresponding voice or data interface, for example, synthesized speechor text messages. The Mobile Position Gateway is neither equipped withthis capability, nor intended for use in such a manner in a wirelessnetwork. The Message Processing engine 408 handles the sending andreceiving of Call Origination/Termination Request, CallOrigination/Termination Response, Position Request and Position Responsemessages. The Call Processing and the Message Processing engines maycommunicate on an internal interface to facilitate the NAC process, forexample, to detect that a calibration call has ended. The interfacebetween these engines also makes use of the Call Origination/TerminationRequest and Response messages.

There are different ways to initiate/terminate the NAC process based onthe calibration calls or Message exchanges, including but not limitedto:

A Messaging Only Method: With the Messaging Only method, the NAC processis triggered and terminated via the Message Interface 404 by CallOrigination/Termination messages from a Mobile Switching Center. Thedetails are described below with reference to FIGS. 5, 6 and 7.

A Call Path Method: With the Call Path method, a calibration call ismade directly to the NAC system (forwarded from the Mobile SwitchingCenter). The NAC process is triggered and terminated via the Call PathInterface 402. The details are described below with reference to FIGS.8, 9 and 10.

A Hybrid Method: With the Hybrid method, the NAC process is triggeredvia the Message Interface 404 but terminated via the Call Path Interface402. The details are described below with reference to FIGS. 11, 12 and13.

After the NAC process is triggered, the NAC system 400 begins sendingmultiple Position Request messages in rapid sequence to the PositionDetermination Device 208. After sending a Position Request message tothe Position Determination Device, the NAC system waits for a responsemessage. When the system receives a Position Response message, it logsthe message and immediately sends another Position Request message. Thisprocess may be implemented sequentially using a single calibration callby a single handset. Alternatively, more than one calibration calls madeby a plurality of handsets may be processed in parallel. PositionMessages are always sent on the Message Interface 404 between the NACsystem 400 and the Position Determination Device 208, regardless of themethod used to trigger/terminate the process. The processing within theNAC system may be stopped after generation of a sufficient amount ofsamples. Alternatively, the process may continue indefinitely or untilthe call is terminated.

The NAC system 400 makes a plurality of Position Determination Requestsfor each Call Origination Request. The system allows a substantialnumber of Position Requests to be generated for statistical significancewhile only requiring the tester to make a single call. This speeds upthe process significantly and saves time.

The system also has accurate knowledge of when the PositionDetermination Device 208 has completed its position computations throughhaving received the Position Response message (the Position Responsemessage is generated by the Position Determination Device 208 when ithas completed its position computations), therefore, minimizing theamount of time between subsequent requests. This eliminates significantuncertainty on the part of a tester who is making calibration calls,wherein the tester does not have specific information about the time ittakes to make a location fix by the Position Determination Device 208.When the call path interface is utilized during a calibration call theNAC system can provide immediate feedback as to the status of messagesvia audible mechanisms inherent to the handset 114, for example,synthesized audio.

In one embodiment, the NAC system 400 terminates the Position Requestgeneration process when the calibration call is ended, which overcomes asignificant challenge wherein Position Request messages would continueto be generated after a calibration call has ended or the handset is nolonger available. The NAC process may also be terminated after aspecified number of requests have been made.

For the Messaging Only method, as shown in FIG. 5, the NAC system 400includes the Message Interface 404 and Message Processing engine 408.The Call Path Interface 402 and Call Processing engine 406 are notrequired in this embodiment. The Mobile Switching Center 202 sends aCall Origination Request message to the NAC system 400. Then the NACsystem returns a Call Origination Response message to the MobileSwitching Center 202 on the same messaging interface so that the callcan be forwarded to the wireline voice or data network. The NAC processis subsequently triggered. The NAC process may be stopped aftergeneration of a sufficient amount of samples, or the process maycontinue until a Call Termination Request message is received from theMobile Switching Center 202.

FIG. 6 presents a process flow chart based on the Messaging Only method.The process begins with block 602 where the NAC system 400 waits for aCall Origination Request message from the Mobile Switching Center 202.In block 604, the NAC system determines if a Call Origination Requesthas been received. If not, the process goes back to block 602 and waits.If the Call Origination Request has been received, in block 606, the NACsystem 400 sends a Call Origination Response to the Mobile SwitchingCenter 202 (so that the Mobile Switching Center can forward the call toits destination). Then in block 608, the NAC system 400 sends a PositionRequest to the Position Determination Device 208. This causes thePosition Determine Device 208 to generate the necessary information andcalculate the position of the handset 114 that placed the call.

Upon successful completion of position calculation, the PositionDetermination Device 208 sends a Position Response message back to theNAC system 400. In block 610, the NAC system waits for the PositionResponse message from the Position Determination Device 208 or a CallTermination request message from the Mobile Switching Center 202. Afterthe NAC system 400 receives a Position Response message in block 612,the process goes back to block 608 and sends another Position Request.Finally, after the NAC system 400 receives a Call Termination Requestmessage from the Mobile Switching Center 202 in block 614 indicatingthat the test is complete, the process stops.

FIG. 7 presents the corresponding state machine. The start state 702 isto wait for a Call Origination Request message from the Mobile SwitchingCenter 202. When a call is placed from a cellular handset 114, theMobile Switching Center 202 sends a Call Origination Request message tothe NAC system 400.

The next state 704 is to send a Call Origination Response message backto the Mobile Switching Center 202 for the call to be quickly forwardedto the destination . The next state 706 is to send a Position Requestmessage to the Position Determination Device 208. This message causesthe Position Determination Device 208 to calculate the position of thecellular handset 114 that placed the call.

The next state 708 is to wait for either a Position Response messagefrom the Position Determination Device 208 or a Call Termination messagefrom the Mobile Switching Center 202. A Position Response message issent by the Position Determination Device 208 when it has finishedcalculating the position of the cellular handset 114 and contains thecalculated position. If this message is received then go to state 706.Alternatively, a Call Termination Request message is sent by the MobileSwitching Center 202 when the call is terminated.

The final state 710 is to send a Call Termination Response message backto the Mobile Switching Center 202. This confirms that the activityassociated with this call has been concluded. This is followed by areturn to the start state 702.

For the Call Path method, as shown in FIG. 8, the NAC system 400 usesCall Path Interface 402 to communicate with the Mobile Switching Center202, and uses Message Interface to communicate with the PositionDetermination Device 208. In this embodiment, a calibration call is madedirectly to the NAC system 400 from the Mobile Switching Center 202; itis received by the Call Processing Engine. The Call Processing engine406 handles the received signal and sends a Call Origination message tothe Messaging Processing engine, as is done between the MSC and the NACsystem for the Messaging Only method. This triggers the NAC process. TheNAC process may be stopped after generation of a sufficient amount ofsamples. Alternatively, the process may continue until the CallProcessing engine 406 generates a Call Termination message to theMessaging Processing engine 408 as the call is released or terminated(the calibration call is ended by the tester)

FIG. 9 presents a process flow chart based on the Call Path method. Asshown, the process begins with block 902 where the NAC system 400 waitsfor a calibration call. Upon the receipt of a calibration call, the CallProcessing engine 406 generates a Call Origination message within block904. Then in block 608, the NAC system 400 sends a Position Request tothe Position Determination Device 208. This causes the PositionDetermination Device 208 to gather the necessary information andcalculate the position of the handset 114 that placed the call.

When the position calculation is successfully completed, the PositionDetermination Device 208 sends a Position Response message back to theNAC system 400. In block 910, the NAC system waits for the PositionResponse message from the Position Determination Device 208, or calltermination or release of the Call Path Interface (indicating thecalibration call is ended, whereby the Call Path corresponding to thecalibration call is released by the Mobile Switching Center 202). In thelatter case, the system monitors the call path from the MSC anddetermines when that call path is released by the MSC. After the NACsystem 400 receives a Position Response message in block 612, theprocess goes back to block 608 and sends another Position Request. Block914 checks if the call to NAC system is terminated. Upon the calltermination in block 916, the Call Processing engine generates a CallTermination message to the Message Processing engine. This indicatesthat the test is completed and the process stops.

FIG. 10 presents the corresponding state machine. The start state 1002is to wait for a calibration call forwarded from the Mobile SwitchingCenter 202 to the NAC system 400. The next state 1004 is to process thereceived signal and generate a Call Origination message by the CallProcessing engine 406. The Call Origination message is sent to theMessaging Processing Engine 408 via an internal interface, and thistriggers the NAC process.

The next state 706 is to send a Position Request message to the PositionDetermination Device 208. This message causes the Position DeterminationDevice 208 to calculate the position of the cellular handset 114 thatplaced the call. The next state 1008 is to wait for either a PositionResponse message from the Position Determination Device 208 or the Callto NAC terminated. A Position Response message is sent by the PositionDetermination Device 208 when it has finished calculating the positionof the cellular handset 114 and contains the calculated position. Whenthis message is received, then go to state 706. When, a call terminationor release of the Call Path Interface occurs, then go to the final state1010.

The final state 1010 is to generate a Call Termination message by theCall Processing engine 406 upon call termination. The Call Terminationmessage is sent to the Message Processing engine 408 via an internalinterface. This concludes the NAC process and the process returns to thestart state 1002.

For the Hybrid method, as shown in FIG. 11, the NAC system 400 uses boththe Call Path Interface 402 and the Message Interface 404 to communicatewith the Mobile Switching Center 202, and also uses the MessageInterface to communicate with the Position Determination Device 208. Inthis embodiment, when a call is placed from a handset 114 to the NACsystem, the Mobile Switching Center 202 sends a Call Origination Requestmessage to the NAC system 400. Then the NAC system returns a CallOrigination Response message to the Mobile Switching Center, and thismessage contains information that causes the Mobile Switching Center toalso route the call to the NAC system. The NAC process is subsequentlytriggered. The NAC process may be stopped after generation of asufficient amount of samples, or the process may continue until the CallProcessing engine 406 generates a Call Termination message to theMessage Processing engine 408 as the call to NAC is released orterminated.

FIG. 12 depicts a process flow chart based on the Hybrid method. Theprocess begins with block 602 where the NAC system 400 waits for a CallOrigination Request message from the Mobile Switching Center 202. Inblock 604, the NAC system determines if a Call Origination Request hasbeen received. If not, the process goes back to block 602. If a CallOrigination Request has been received, the process goes to block 1206where the system sends a Call Origination Response to the MobileSwitching Center 202 (and this response message causes the MobileSwitching Center 202 to also forward the call to the NAC system's Callinterface 402. Then in block 608, the NAC system 400 sends a PositionRequest to the Position Determination Device 208. This causes thePosition Determination Device 208 to gather the necessary informationand calculate the position of the handset 114 that placed the call.

When the position calculation is successfully completed, the PositionDetermination Device 208 sends a Position Response message back to theNAC system 400. In block 910, the NAC system waits for the PositionResponse message from the Position Determination Device 208, or calltermination or release of the Call Path Interface from the MobileSwitching Center 202. After the NAC system 400 receives a PositionResponse message in block 612, the process goes back to block 608 andsends another Position Request. In Block 914, the process checks if thecall to NAC is terminated. Upon call termination (the tester has endedthe call, and the Call interface is released) in block 916, the CallProcessing engine generates a Call Termination message to the MessageProcessing engine indicating that the test is complete, and the processstops.

FIG. 13 presents the corresponding state machine. As shown, the startstate 702 is to wait for a Call Origination Request message from theMobile Switching Center 202. When a call is placed from a cellularhandset 114 to the NAC system 400, the Mobile Switching Center 202 sendsa Call Origination Request message to the NAC system 400.

The next state 1304 is to send a Call Origination Response message backto the Mobile Switching Center 202. This response message contains theinformation that requires the Mobile Switching Center 202 to also routethe call to the NAC system 400. The next state 706 is to send a PositionRequest message to the Position Determination Device 208. This messagecauses the Position Determination Device 208 to calculate the positionof the cellular handset 114 that placed the call.

The next state 1008 is to wait for either a Position Response messagefrom the Position Determination Device 208 or the call to NACterminated. A Position Response message is sent by the PositionDetermination Device 208 when it has finished calculating the positionof the cellular handset 114 and contains the calculated position. Ifthis message is received then go to state 706. Alternatively, a calltermination or release of the Call Path Interface leads to the finalstate 1010.

The final state 1010 is to generate a Call Termination message by theCall Processing engine 406 upon call to NAC termination. The CallTermination message is sent to the Message Processing engine 408 via aninternal interface. This concludes the NAC process and the processreturns to the start state 702.

The result of the NAC process is a log file generated by the PositionDetermination Device that contains a significant number of calibrationsamples generated over a certain time period, which is significantlymore than the number of calibration samples that can be generatedwithout a NAC system over the same time period. These calibrationsamples are used externally to the NAC system in order to determine thecalibration values as described in the background of the invention. Thekey to generating significantly more calibration samples than ispossible without NAC is the plurality of Position Request messages thatis generated per call (the number of messages that can be generated percall is not bounded). Furthermore, the fact that the NAC processrecognizes when each location is completed significantly reduces thetime required to obtain a single sample, thus resulting in a significanttime savings as compared to methods subject to uncertainty of processingtime required by the Position Determination Device.

When the call path method or hybrid method embodiments described hereinare used, the audible feedback mechanisms to the handset, and hence thetester, are also enabled via the triggers used to start the NAC process.In this case, the handset is provided with a synthesized speechgenerated by the NAC system, which entails notifying the tester of theprogress of the NAC process. For example, the tester hears “sample 1complete, calibration call location is <Latitude and Longitude oflocation of the calibration sample 1>; sample 2 complete calibrationcall location is <Latitude and Longitude of location of the calibrationsample 2>; etc. This audible feedback mechanism continues throughout theduration of the calibration call. The location associated with acalibration sample is generated from the log file, which is output fromthe NAC system. An example of this log file is shown in FIG. 14.

In one embodiment, the log file is generated from the Position Requestand Position Response messages. The Position Request Message contains atelephone number that identifies the handset that made the calibrationcall, which is used by the Position Determination Device 208 to locatethe correct handset. The Position Response Message sent in response tothe Position Request message contains the latitude and longitude of thehandset for that calibration sample. This facilitates synthesizing thespeech that provides the audible feedback to the handset/tester. A logfile entry is created for each handset used to make calibration calls.

It will be recognized by those skilled in the art that variousmodifications may be made to the illustrated and other embodiments ofthe invention described above, without departing from the broadinventive scope thereof. It will be understood therefore that theinvention is not limited to the particular embodiments or arrangementsdisclosed, but is rather intended to cover any changes, adaptations ormodifications which are within the scope and spirit of the invention asdefined by the appended claims.

1. A method for calibrating a wireless network including a positiondetermination device (PDD), the method comprising: continuouslygenerating and sending a plurality of position request messages to thePDD in response to a request trigger; continuously receiving a pluralityof position request responses from the PDD in response to the pluralityof position request messages; receiving a termination trigger;terminating the generating and sending of the plurality of subsequentposition request messages when the termination trigger is received; andsending a termination message in response to the received terminationtrigger.
 2. The method of claim 1, further comprising causing thegeneration of output data for use in network calibration.
 3. The methodof claim 1, wherein the termination trigger is a call terminationmessage from a mobile switching center.
 4. The method of claim 1,wherein the termination trigger is release of a received phone call. 5.The method of claim 1, further comprising generating a synthesized audiofeedback.
 6. The method of claim 1, further comprising: receiving aphone call; sending a first position request message to the PDD inresponse to the received phone call; receiving a position responsemessage from the PDD; and sending a second position request message tothe PDD in response to the same received phone call and the receivedposition response message.
 7. A system for calibrating a wirelessnetwork including a Position Determination Device (PDD) comprising:means for continuously generating and sending a plurality of positionrequest messages to the PDD in response to a request trigger; means forcontinuously receiving a plurality of position request responses fromthe PDD in response to the plurality of position request messages; meansfor receiving a termination trigger; means for terminating thegenerating and sending of the plurality of subsequent position requestmessages when the termination trigger is received; and means for sendinga termination message in response to the received termination trigger.8. The system of claim 7, further comprising means for causing thegeneration of output data for use in network calibration.
 9. The systemof claim 7, wherein the termination trigger is a call terminationmessage from a mobile switching center.
 10. The system of claim 7,wherein the termination trigger is release of a received phone call. 11.The method of claim 7, further comprising generating a synthesized audiofeedback.
 12. The system of claim 7, further comprising: means forreceiving a phone call; means for sending a first position requestmessage to the PDD in response to the received phone call; means forreceiving a position response message from the PDD; and means forsending a second position request message to the PDD in response to thesame received phone call and the received position response message. 13.A method for calibrating a wireless network including a positiondetermination device (PDD), the method comprising: continuouslygenerating and sending a plurality of position request messages to thePDD in response to request trigger; continuously receiving a pluralityof position request responses from the PDD in response to the pluralityof position request messages; generating a calibration sample as adifference between an absolute time reference and an actual timereference for each received position request response; and aggregatingthe calibration samples for the plurality of received position requestresponses to generate a calibration value.
 14. The method of claim 13,further comprising generating a termination trigger to terminate thegeneration and sending of the plurality of position request messages.15. The method of claim 14, wherein the termination trigger is a calltermination message from a mobile switching center.
 16. The method ofclaim 14, wherein the termination trigger is release of a received phonecall.
 17. The method of claim 13, further comprising generating asynthesized audio feedback.
 18. The method of claim 13, furthercomprising: receiving a phone call; sending a first position requestmessage to the PDD in response to the received phone call; receiving aposition response message from the PDD; and sending a second positionrequest message to the PDD in response to the same received phone calland the received position response message.